The Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS) is a 10-item functional inventory which was devised for use in therapeutic trials in ALS. Each item is rated on a 0-4 scale by the patient and/or caregiver, yielding a maximum score of 40 points. The ALSFRS assesses patients' levels of self-sufficiency in areas of feeding, grooming, ambulation and communication. Rotated factor analysis of the ALSFRS found that the rating items group logically and consistently into four categories. The ALSFRS has been validated both cross-sectionally and longitudinally against muscle strength testing, the Schwab and England ADL rating scale, the Clinical Global Impression of Change (CGIC) scale, and independent assessments of patient's functional status. In this report, we use the data provided by the placebo patients who participated in the ALS CNTF Treatment Study (ACTS) to demonstrate the robustness, test-retest reliability and consistency of the ALSFRS as employed in a large, multicenter clinical trial.